Hectograph blanket and method of treating same



Patented Sept. 1 1942 j I UNITED. STATE s PATIENT OFFICE HECTOGRAPH BLANKET AND METHOD OF TREATING- SAME William J. Champion, Chicago, Ill., 'assignor' to Ditto, Incorporated, Chicago, 111., a corporation of West Virginia No Drawing. Application August 4, 1941, .Serial No. 405,406

6 Claims.

are directly exposed to the action of the atmosphere and therefore any absorption of moisture will occur there. will cause swelling of the gelatin on the edges and consequently the pressure on winding the hectograph roll will become concentrated there. The absorption of moisture at the edges will soften the mass, thus rendering the mass at the extreme edges very sensitive to thermal or mechanical action. The duplication mass at the edges is not braced on the outer side and consequently is liable to give way in that direction if exposed to extreme pressure or if abnormally softened.

For the above reasons, it is highly desirable to strength the edges of hectograph rollsuand a principal object of this invention is to provide a hectograph blanket having strengthened edges. In accordance with this invention, the hectograph copy mass is rendered mechanically more resistant by tanning the copy mass to a greater extent on the edge portions than in the central portion, thereby providing a hectograph blanket having optimum copying qualities on its central portion and having the extreme edges tanned so as to give them extreme mechanical resistance while retaining copying qualities which are adequate although-not necessarily quite as good as the central portions of the mass.

The tanning agent may be applied by brushing a, solution of the tanning agent along the edges of an ordinary hectograph blanket which may be moderately tanned at least in the central portions by means of an aldehyde tanning agent such as formaldehyde. 7

While any tanning agent applied to the margins or the edges of a hectograph roll results in locally enhanced resistance, for best results the agent selected must meet rather rigid requirements, namely: (1) It must be capable of penetrating the mass all the -way through to the backing so as to enhance the resistance of the entire edge; (2) Once applied, it must not Such absorption of moisture be weakened or removed by subsequent conditioning or applications of water, nor by "sweating" or syneresis; (3) Once it has reacted with the protein components of the mass. it must remain localized and must not continue to diffuse or to spread through the mass over any period of time.

While some benefits have been derived by the application of metallic taning agents of the general class of chromium salts,, aluminum salts, zirconyl salts, iron salts or the like, these substances generally are not preferred because they tend to react with the protein components before penetration to the backing is completed. While sulfonated compounds of the type exemplified by Aerosols and tergitols, or aldehyde compositions such as hexa methylene tetramine, formaldehyde, aldols, and the like, give practically applicable results, they are generally not preferred because they have a tendency to continue diffusing through the mass after application so as to cause a gradual hardening of the entire mass over a period of several months or a year.

For the purpose of this invention, I prefer to use an agent which is in itself substantially I-non-tanning but which over a period of time, such as a few days or weeks, is transformed into one of those tanning agents which have strictly localized action and do not diffuse but which if applied as such would be deficient in penetration of the mass. For example, I could apply a substantially non-tanning, unstable compound of chromium, aluminum, zirconyl, or other metal tanning agents of similar action, which over a period of time decomposes to form a tanning compound of these metals. I have found that, for example, alkali bichromates are highly suitable for this purpose. If applied in a solution of concentration from .01 to 6% or preferably about 0.5% to the edges of the hectograph roll, the alkali bichromates penetrate the hectograph mass where applied, evenly, throughout the entire thickness of the mass, initially without tanning action and are subsequently over a period of a few days reduced to chromic salts which are non-diffusing tanning agents of strictly l0- calized action. In this manner the edge of the hectograph roll is rendered extremely resistant while retaining good copying properties. The edge protectingsolution may be applied either on the conveyor when the rolls are being made, or preferably shortly thereafter, when the gelatin is set. The application may be made with a solution of, for example, 1% sodium bichromate by means of a wick, or roller type applier art. Also the tanning agent may be applied at the slitting knives when the backing is slit, or otherwise to the edges of the backing, and the hectograph composition is then applied subsequently. In this event, I'prefer to use tanning agents in a more concentrated solution. In many cases, however, it is most convenient to apply this protective taming solution to the edges of the hectograph roll after the roll has been wound up.

For this purpose, it is desirable to modify the viscosity of the tanning solution. If this is not done, the solution may in some spots, where the winding is not perfect, penetrate between the layers of the wound up roll and cause extensive surface tanning in more. central portions. To avoid this, I prefer to add to the tanning solution a viscosity imparting agent in such amounts that the resulting tanning solution does not flow into the interior of the roll but only penetrates at the extreme margins where pressure can be applied to it, or where it can be rubbed in. -Suitable viscosity imparting agents are, for example, methyl celluloses, pectins, gums, bentonite, starches,

starch glycerides, and the like.

The invention is illustrated by the following specific examples which aregiven by way of i1- lustration only and not in any sense of limitation:

Example I To a freshly prepared hectograph roll, the following solution was applied along the margins to cover A" on each margin: 1% sodium dichromate in water. This solution was applied by means of wicks which were kept in frictional engagement withthe edges of the roll, as this was being moved on the conveyor. The roll thus treated was allowed to stand sufiiciently long for the liquid to become absorbed, or to dry, and was then wound up in the usual manner.

Example II Each one of the following compositions: I (A)' An aqueous acid solutioncontaining Percent Potassium dichromate 0.25 Dow Methocel 1500 CPS 2.00 Water 97.75

, An aqueous acid solution containing Percent Citrus pectin 5.0 Ammonium dichromate 0.5 Water 94.5

Percent Dow Methocel 100 CPS 4 Potassium dichromate 1 Water 95 was applied to the end of a rolled up hectograph blanket, for example, by brushing onto the edges. The rolls thus treated were allowed to stand for the usual aging period of several weeks. On inspection, they were found to be hardened on the edges so as to withstand drastic hydrothermal conditions, and mechanical abuse.

Example III The edges of fibre roll backing were brushed with a solution of 12% ammonium bichromate in water, and rolls were made in the conventional manner, using this backing material. The rolls thus produced were found to have highly resistant edges.

Example IV The following solution was applied to the edge of a hectograph blanket, covering a distance of A" on each margin:

Percent Aerosol O. T 3 Water 85 Ethanol l2 2 The roll thus treated was allowed to stand twenty-four hours and then wound up in the usual manner.

Example V The edges of cloth roll backing were brushed with a solution containing:

. K. Percent Aerosol 4 Naphthenic id 10 Thin nitro cellulose lacquer 86 after passing over a slitting knife, so that a martions. Changes, therefore, may be made without 2. A hectograph blanket having a copy masscomprising a gelatin gel which is tanned to a greater extent on the edges than in the central portion, said edge portion comprising a reaction product of gelatin and an inorganic tanning agent.

3. A hectograph blanket having a copy mass comprising a gelatin gel including a central portion of a elatin-aldehyde reaction product and a marginal edge portion of a reaction product of gelatin with a salt of an element selected from the group consisting of chromium, aluminum and zinc.

4. A hectograph blanket having a gelatinous copy mass which is tanned to a greater extent on the edge portion than in the central portion, said tanned edge portion comprising the reaction product of gelatin with a chromium salt.

5. The method of improving mechanical resistance of hectograph blankets which comprises applying to the edges of a hectograph copy mass an agent which itself is substantially non-tanning but which over a period of time is transformed into a tanning agent.

6. The method of improvin the mechanical resistance of a hectograph blanket which comprises applying a solution of an alkali dichromate to the edges of a, hectograph copy mass.

WILLIAM J. CION. 

